The present invention relates to an electro-photographic copying machine of the scanning exposure type wherein a photosensitive member is exposed to a document image by a scanning system to form an image corresponding to the document image on the member, and the image is then transferred onto a copy sheet. More particularly, the invention relates to a scanning means control system which is advantageous for use in such a copying machine to shift the image to be formed on the copy sheet from the image position on the document in the direction of scanning.
U.S Pat. No. 4,260,242 (Apr. 7, 1981) and U.S. Pat. No. 4,451,136 (May 29, 1984) disclose copying machines which are adapted to shift images in such a manner for edition.
These machines are designed to vary the registration timing for a copy sheet to be fed to the position where the image on the photosensitive member is transferred onto the copy sheet.
This will be described specifically with reference to a document M shown in FIG. 1 (a) and having an image A, and with a copy sheet P, shown in FIG. 1 (b), on which the document image A is to be formed as a copy image A'.
When the document M of FIG. 1 (a) is scanned in the direction of arrow b from its right end, an image is formed on the copy sheet P of FIG. 1 (b) from its right end in the same direction as the scanning direction. In the case of usual registration timing, the position of the image A' formed on the sheet P corresponds to the position of the image A on the document M. However, the copy sheet P is 1/2 the size of the document M in the scanning direction. It is therefore the image portion of the document M over a scanning length Sno corresponding to the size of the copy sheet P that can be reproduced on the sheet P with the usual timing, and it is impossible to copy the image A of the document M on the sheet P.
Accordingly, if the registration timing is delayed by an amount corresponding to 1/2 the size of the document M in the scanning direction, the document image can be shifted on the copy sheet P in the scanning direction. Thus, the image A on the document M is formed as the copy image A' in the illustrated position on the sheet P.
The document image can be copied as shifted in this way only when the image is within the scanning range. Accordingly, even if one attempts to employ the system disclosed in U.S. Pat. No. 4,211,482 (Jul. 8, 1980) which is adapted to determine the scanning length from the copy sheet size and the magnification to avoid useless scanning action outside the required range and needless waste of time, the machine fails to reproduce the image outside the area specified by the system according to the sheet size and the magnification. Such a failure could be avoided by an operator setting the desired scanning length, but that procedure is cumbersome and inefficient.